1. FIELD OF THE INVENTION
The present invention relates to a fuel cell, and more particularly, the present invention concerns a fuel cell which is improved in the gas sealing characteristics of the periphery of a flow passage formed by a gas separating plate.
2. DESCRIPTION OF THE RELATED ART
FIG. 1 is a cross-sectional view of a conventional laminated type fuel cell which employs an inner manifold process. Such a fuel cell is disclosed in the specification of, for example, Japanese Patent Application Laid-Open No. 62-208559. This fuel cell is comprised of an electrolyte layer 10 and a pair of electrode reacting portions 11 and 12 disposed in opposed relation with the electrolyte layer 10 interposed therebetween. The electrode reacting portion 11 is an oxidizing agent electrode reacting portion where oxidant gas A mainly composed of air and carbon dioxide is electrochemically reacted with the electrolyte, and the electrode reacting portion 12 is a fuel electrode reacting portion 12 in which electrochemical reaction of a fuel gas B mainly composed of hydrogen, carbon monoxide and hydrocarbon occurs. The electrode reacting portions 11 and 12 respectively incorporate corrugated plates that form gas flow passages 11a and 12a. The gas fluids A and B are separated from each other by a gas separating plate 13, which is called a bipolar or separator plate. A fuel cell is formed by laminating the electrolyte layer 10, the gas separating plate 13 and so on successively.
FIG. 2 is an exploded perspective view of the gas separating plate 13 that forms gas flowing passages in the laminated type fuel cell shown in FIG. 1. Since this fuel cell is of a parallel flow type in which the gas fluids A and B flow parallel to each other, manifolds 16a and 17a for supplying the gas fluids A and B are alternately provided on one side of the periphery of the gas separating plate 13, while exhaust manifold 16b and 17b are alternately disposed on the side opposite to that on which the supply manifolds 16a and 17a are provided. On both sides of the periphery of the separating plate 13, the supply manifolds 16a and 17a and the exhaust manifolds 16b and 17b are respectively separated from each other by distance pieces 14 and 15. Further, the irregularities of the corrugated plates of the electrode reacting portions 11 and 12 respectively form the gas flow passages 11a and 12a, as stated above.
In the thus-arranged fuel cell, the laminated layers are pressurized to compress the layers of the lamination so that an appropriate bearing pressure can be applied to the laminated surfaces. This allows the contact portions of the laminated members to be sealed, thus preventing gas leakage.
Next, the operation of the conventional laminated type fuel cell will be described below. The oxidant gas A which is supplied from below as viewed in FIGS. 1 and 2 passes through the oxidant gas supply manifolds 16a that are opened in the distance pieces 15 disposed below the gas separating plates 13, and flows into the gas flow passages 11a of the oxidant electrode reacting portions 11. The oxidant gas A that has flown through the gas flow passages 11a is exhausted to the outside of the cell through the exhaust manifolds 16b. In contrast, the fuel gas B which is supplied from below flows into the upper portions of the gas separating plates 13 through the supply manifolds 17a which are the small holes formed in the distance pieces 15 disposed below the gas separating plates 13. The fuel gas B is then supplied into the gas flow passages 12a of the fuel electrode reacting portions 12 through the fuel gas supply manifolds 17a opened in the distance pieces 14 disposed above the gas separating plates 13.
In the above-described laminated type fuel cell, improvement in the gas sealing and balancing of the bearing pressure are essential to the prevention of gas leakage and reduction in the performance of the cell. However, the electrode reacting portions, the gas supply manifolds and the gas sealed portions provided around the gas supply manifolds show different creep (plastic deformation) characteristics with the passage of time, and the creep or deformation caused in the electrode reacting portions therefore generates unbalance in the bearing pressure or gas leakage. In relation to this, Japanese patent Application Laid-Open No. 62-188177 filed by the applicants of this invention discloses a fuel cell of the type in which gas fluid is supplied using outer manifolds provided at the side of the fuel cell and in which gas separating plates are turned at the sides of the flow passages so as to make them flexible.
In a laminated type fuel cell in which gas fluid is supplied using the inner manifolds, the walls of the inner manifolds are in direct contact with the external atmosphere, and the sealed portions of the manifolds are in contact with the other gas flow passages, thus necessitating more reliable sealing. However, in such a type of conventional fuel cell, it is impossible to make sure that the sealed portions deform uniformly in accordance with the deformation of the electrode reacting portions caused by the creep, causing mixture and reaction of the fuel gas with the oxidant gas in a fuel cell.